US 7184869 B2 Abstract In steering control for individually controlling wheel steering angles α
_{1}, α_{2}, α_{3}, and α_{4 }of a vehicle in accordance with a condition equation for forming a prescribed mode, one of the condition equation variables is used as a steering command value S. In a process for changing the command value S from a value S_{1 }to a value S_{2}, for transitioning the steering angles α_{1}, α_{2}, α_{3}, α_{4 }from values [α_{1}, α_{2}, α_{3}, α_{4}]_{S1 }corresponding to the steering command value S_{1}, to values [α_{1}, α_{2}, α_{3}, α_{4}]_{S2 }corresponding to the steering command value S_{2}, the steering angles α_{1}, α_{2}, α_{3}, α_{4 }are changed toward incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+ΔS }corresponding to a steering command value (S_{1}+ΔS), which is the steering command value S_{1 }to which an incremental steering command value ΔS has been added. After the steering angles α_{1}, α_{2}, α_{3}, α_{4 }reach their incremental transition steering angles and steering angle conformance is detected, the angles are changed toward incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+nΔS }corresponding to a steering command value (S_{1}+nΔS), which is the steering command value to which an incremental steering command value ΔS has been added [n times] in succession. This is repeated as many times as required to change the steering angles α_{1}, α_{2}, α_{3}, α_{4 }from [α_{1}, α_{2}, α_{3}, α_{4}]_{S1 }to [α_{1}, α_{2}, α_{3}, α_{4}]_{S2}.Claims(20) 1. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value S and changing the steering command value S from a value S
_{1 }to a value S_{2};(b) computing incremental transition steering angles of four wheels [α
_{1}, α_{2}, α_{3}, α_{4}]_{S1+ΔS }corresponding to a steering command value (S_{1}+ΔS), which is the steering command value S_{1 }to which an incremental steering command value ΔS has been added, in accordance with the steering constraint condition equations;(c) changing steering angles of the four wheels α
_{1}, α_{2}, α_{3}, α_{4 }toward the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{S1+ΔS};(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+ΔS};(e) computing next incremental transition steering angles [α
_{1}, α_{2}, α_{3}, α_{4}]_{S1+2ΔS }corresponding to a steering command value (S_{1}+2ΔS), in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }toward the next incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+2ΔS};(g) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the next incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+2ΔS}; and(h) repeating above Steps (e)–(g) until the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }reach steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{S2 }corresponding to the steering command value S_{2}.2. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value S and changing the steering command value S from a value S
_{1 }to a value S_{2};(b) computing incremental transition steering angles of four wheels [α
_{1}, α_{2}, α_{3}, α_{4}]_{S1+ΔS }and incremental transition speeds of rotation of the four wheels [n_{1}, n_{2}, n_{3}, n_{4}]_{S1+ΔS }corresponding to a steering command value (S_{1}+ΔS), which is the steering command value S_{1 }to which an incremental steering command value ΔS has been added, in accordance with the steering constraint condition equations;(c) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+ΔS }and the incremental transition speeds of rotation [n_{1}, n_{2}, n_{3}, n_{4}]_{S1+ΔS}, respectively;(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+ΔS};(e) computing next incremental transition steering angles [α
_{1}, α_{2}, α_{3}, α_{4}]_{S1+2ΔS }and next incremental transition speeds of rotation [n_{1}, n_{2}, n_{3}, n_{4}]_{S1+2ΔS }corresponding to a steering command value (S_{1}+2ΔS), respectively, in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and the speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward the next incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+2ΔS }and the next incremental transition speeds of rotation[n_{1}, n_{2}, n_{3}, n_{4}]_{S1+2ΔS}, respectively;(g) detecting a steering angle conformance, wherein the steering angles of the four wheels α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles of the four wheels [α_{1}, α_{2}, α_{3}, α_{4}]_{S1+2ΔS}; and(h) repeating above Steps (e)–(g) until the steering angles of the four wheels α
_{1}, α_{2}, α_{3}, α_{4 }reach the steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{S2 }corresponding to the steering command value S_{2}.3. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value R which is a distance between a point central to positions of four wheels and a center point of concentric arcs, and changing the steering command value R from a value R
_{1 }to a value R_{2};(b) computing incremental transition steering angles of the four wheels[α
_{1}, α_{2}, α_{3}, α_{4}]_{R1+ΔR }corresponding to a steering command value (R_{1}+ΔR), which is the steering command value R_{1 }to which an incremental steering command value ΔR has been added,in accordance with the steering constraint condition equations;(c) changing the steering angles of the four wheels α
_{1}, α_{2}, α_{3}, α_{4 }toward the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R1+ΔR};(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R1+ΔR};(e) computing next incremental transition steering angles[α
_{1}, α_{2}, α_{3}, α_{4}]_{R1+2ΔR }corresponding to a steering command value (R_{1}+2ΔR), in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }toward the next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R1+2ΔR};(g) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R1+2αR}; and(h) repeating above Steps (e)–(g) until the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }reach the steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R2 }corresponding to the steering command value R_{2}.4. A four-wheel-independent-steering-vehicle steering control method as recited in
where
α
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
W is the distance between each wheel and a center line Y between the left wheels and right wheels; and
R, which is used as the steering command value, is the distance between a point central to the positions of the four wheels and a center point of the concentric arcs.
5. A four-wheel-independent-steering-vehicle steering control method as recited in
α _{3}=α_{4}=0where
α
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
W is the distance between each wheel and a center line Y between the left wheels and right wheels; and
R, which is used as the steering command value, is the distance between a point central to the positions of the four wheels and a center point of the concentric arcs.
6. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value R which is a distance between a point central to positions of four wheels and a center point of concentric arcs, and changing the steering command value R from a value R
_{1 }to a value R_{2};(b) computing incremental transition steering angles of the four wheels [α
_{1}, α_{2}, α_{3}, α_{4}]_{R1+ΔR }and incremental transition speeds of rotation of the four wheels[n_{1}, n_{2}, n_{3}, n_{4}]_{R1+ΔR }corresponding to a steering command value (R_{1}+ΔR), which is the steering command value R_{1 }to which an incremental steering command value ΔR has been added, in accordance with the steering constraint condition equations;(c) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{R1+ΔR }and the incremental transition speeds of rotation [n_{1}, n_{2}, n_{3}, n_{4}]_{R1+ΔR}, respectively;(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R1+ΔR};(e) computing next incremental transition steering angles [α
_{1}, α_{2}, α_{3}, α_{4}]_{R1+2ΔR }and next incremental transition speeds of rotation [n_{1}, n_{2}, n_{3}, n_{4}]_{R1+2ΔR }corresponding to a steering command value (R_{1}+2ΔR), respectively, in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and the speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R1+2ΔR};and next incremental transition speeds of rotation[n_{1}, n_{2}, n_{3}, n_{4}]_{R1+2ΔR}, respectively;(g) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R1+2ΔR}; and(h) repeating above Steps (e)–(g) until the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }reach the steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{R2 }corresponding to the steering command value R_{2}.7. A four-wheel-independent-steering-vehicle steering control method as recited in
where
α
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;n
1, n2, n3, and n4 are the speeds of rotation of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
W is the distance between each wheel and a center line Y between the left wheels and right wheels; and
R, which is used as the command value, is the distance between a point central to the positions of the four wheels and a center point of the concentric arcs.
8. A four-wheel-independent-steering-vehicle steering control method as recited in
where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;n
1, n2, n3, and n4 are the speeds of rotation of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
R, which is used as the command value, is the distance between a point central to the positions of the four wheels and a center point of the concentric arcs.
9. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value α
_{n }which is an angle formed between a center line Y between left and right wheels of the vehicle, and a direction of travel of a point P_{n}, and changing the steering command value α_{n }from a value α_{n1 }to a value α_{n2};(b) computing incremental transition steering angles of the four wheels [α
_{1}, α_{2}, α_{3}, α_{4}]_{αn1+Δαn }corresponding to a steering command value (α_{n1}+Δα_{n}), which is the steering command value α_{n1 }to which an incremental steering command value Δα_{n }has been added, in accordance with the steering constraint condition equations;(c) changing the steering angles of the four wheels α
_{1}, α_{2}, α_{3}, α_{4 }toward the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+Δαn};(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+Δαn};(e) computing next incremental transition steering angles[α
_{1}, α_{2}, α_{3}, α_{4}]_{αn1+2Δαn }corresponding to a steering command value (α_{n1}+2Δα_{n}) in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }toward the next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+2Δαn};(g) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+2Δαn}; and(h) repeating above Steps (e)–(g) until the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }reach the steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn2 }corresponding to the steering command value α_{n2}.10. A four-wheel-independent-steering-vehicle steering control method as recited in
where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
W is the distance between each wheel and a center line Y between the left wheels and right wheels;
x
_{n }and y_{n }are the x and y coordinates of an arbitrary point on the vehicle, P_{n}; andα
_{n}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle, and the direction of travel of the point P_{n}.11. A four-wheel-independent-steering-vehicle steering control method as recited in
and
α _{3}=α_{4}=0where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
W is the distance between each wheel and a center line Y between the left wheels and right wheels;
x
_{n }and y_{n }are the x and y coordinates of an arbitrary point on the vehicle, P_{n}; andα
_{n}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle, and the direction of travel of the point P_{n}.12. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value α
_{n }which is an angle formed between a center line Y between left and right wheels of the vehicle, and a direction of travel of the point P_{n}, and changing the steering command value α_{n }from a value α_{n1 }to a value α_{n2};(b) computing incremental transition steering angles of four wheels [α
_{1}, α_{2}, α_{3}, α_{4}]_{αn1+Δα}and incremental transition speeds of rotation of the four wheels [n_{1}, n_{2}, n_{3}, n_{4}]_{αn1+Δα}corresponding to a steering command value (_{αn1}+Δα_{n}), which is the steering command value α_{n1 }to which an incremental steering command value Δα_{n }has been added, in accordance with the steering constraint condition equations;(c) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+Δαn }and the incremental transition speeds of rotation[n_{1}, n_{2}, n_{3}, n_{4}]_{αn1+Δαn}, respectively;(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+Δαn};(e) computing next incremental transition steering angles[α
_{1}, α_{2}, α_{3}, α_{4}]_{αn1+2Δαn }and next incremental transition speeds of rotation[n_{1}, n_{2}, n_{3}, n_{4}]_{αn1+2Δαn }corresponding to a steering command value (α_{n1}+2Δα_{n}), respectively, in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and the speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward the next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+2Δαn }and the next incremental transition speeds of rotation[n_{1}, n_{2}, n_{3}, n_{4}]_{αn1+2Δαn}, respectively;(g) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{αn1+2Δαn}; and(h) repeating above Steps (e)–(g) until the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }reach the steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{αn2 }corresponding to the steering command value α_{n2}.13. A four-wheel-independent-steering-vehicle steering control method as recited in
where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;n
1, n2, n3 and n4 are the speeds of rotation of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
W is the distance between each wheel and a center line Y between the left wheels and right wheels;
x
_{n }and y_{n }are the x and y coordinates of an arbitrary point on the vehicle, P_{n}; and α_{n}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle and the direction of travel of the point P_{n}.14. A four-wheel-independent-steering-vehicle steering control method as recited in
where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;n
1, n2, n3 and n4 are the speeds of rotation of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
W is the distance between each wheel and a center line Y between the left wheels and right wheels;
x
_{n }and y_{n }are the x and y coordinates of an arbitrary point on the vehicle, P_{n}; and α_{n}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle and the direction of travel of the point P_{n}.15. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value α
_{0 }which is an angle formed between a center line Y between left and right wheels of the vehicle, and a direction of travel of a point P_{0 }which is a center point on a line connecting left and right front wheels, and changing the steering command value α_{0 }from a value α_{01 }to a value α_{0 2};(b) computing incremental transition steering angles of the four wheels [α
_{1}, α_{2}, α_{3}, α_{4}]_{α01+Δα0 }corresponding to a steering command value (α_{01}+Δα_{0}), which is the steering command value α_{01 }to which an incremental steering command value Δα_{0 }has been added, in accordance with the steering constraint condition equations;(c) changing the steering angles of the four wheels α
_{1}, α_{2}, α_{3}, α_{4 }toward the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{α01+Δα0};(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{α01+Δαn};(e) computing next incremental transition steering angles [α
_{1}, α_{2}, α_{3}, α_{4}]_{α01+2Δα0 }corresponding to a steering command value (α_{01}+2Δα_{0}) in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }toward the next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{α01+2Δα0};(g) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the next incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{α01+2Δα0}; and(h) repeating above Steps (e)–(g) until the steering angles α
_{n}, α_{2}, α_{3}, α_{4 }reach the steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{α02 }corresponding to the steering command value α_{0 2}.16. A four-wheel-independent-steering-vehicle steering control method as recited in
where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
α
_{o}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle, and the direction of travel of the point Po, which is the center point on a line connecting the left and right front wheels.17. A four-wheel-independent-steering-vehicle steering control method as recited in
and
α _{3}=α_{4}=0where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
α
_{o}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle, and the direction of travel of the point Po, which is the center point on a line connecting the left and right front wheels.18. A four-wheel-independent-steering-vehicle steering control method comprising:
(a) using one of variables of steering constraint condition equations for forming a prescribed steering mode as a steering command value α
_{0 }which is an angle formed between a center line Y between left and right wheels of the vehicle, and a direction of travel of a point P_{0}, which is a center point on a line connecting left and right front wheels, and changing the steering command value α_{0 }from a value α_{01 }to a value α_{02};(b) computing incremental transition steering angles of the four wheels [α
_{1}, α_{2}, α_{3}, α_{4 }]_{α01+Δα01 }and incremental transition speeds of rotation of the four wheels [n_{1}, n_{2}, n_{3}, n_{4}]_{α01+Δα01 }corresponding to a steering command value (α_{01}+Δα_{0}), which is the steering command value α_{01 }to which an incremental steering command value Δα_{0 }has been added, in accordance with the steering constraint condition equations;(c) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{α01+Δα0 }and the incremental transition speeds of rotation [n_{1}, n_{2}, n_{3}, n_{4}]_{α01+Δα0}, respectively;(d) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{α01+Δα0};(e) computing next incremental transition steering angles [α
_{1}, α_{2}, α_{3}, α_{4}]_{α01+2Δα0 }and next incremental transition speeds of rotation [n_{1}, n_{2}, n_{3}, n_{4}]_{α01+2Δαn }an corresponding to a steering command value (α_{01}+2Δα_{0}), respectively, in accordance with the steering constraint condition equations;(f) changing the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }and the speeds of rotation n_{1}, n_{2}, n_{3}, n_{4 }toward the next incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{α01+2Δα0 }and the next incremental transition speeds of rotation[n_{1}, n_{2}, n_{3}, n_{4}]_{α01+2Δα0}, respectively;(g) detecting a steering angle conformance, wherein the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }have reached the incremental transition steering angles [α_{1}, α_{2}, α_{3}, α_{4}]_{α01+2Δα0}; and(h) repeating above Steps (e)–(g) until the steering angles α
_{1}, α_{2}, α_{3}, α_{4 }reach the steering angles[α_{1}, α_{2}, α_{3}, α_{4}]_{α02 }corresponding to the steering command value α_{0 2}.19. A four-wheel-independent-steering-vehicle steering control method as recited in
where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;n
1, n2, n3, and n4 are the speeds of rotation of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
α
_{o}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle, and the direction of travel of the point Po, which is the center point on a line connecting the left and right front wheels.20. A four-wheel-independent-steering-vehicle steering control method as recited in
where
_{1}, α_{2}, α_{3}, and α_{4 }are the steering angles of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;1, n2, n3, and n4 are the speeds of rotation of the right front wheel, left front wheel, right rear wheel, and left rear wheel, respectively;L is the distance between each wheel and a center line X between the front wheels and rear wheels;
_{o}, which is used as the steering command value, is the angle formed between the center line Y between the left and right wheels of the vehicle, and the direction of travel of the point Po, which is the center point on a line connecting the left and right front wheels.Description This application is related to application Ser. No. 10/294,113 entitled “ELECTRIC VEHICLE STEERING/DRIVE CONTROL METHOD, ELECTRIC VEHICLE STEERING/DRIVE CONTROL APPARATUS, AND ELECTRIC VEHICLE”, filed on Nov. 14, 2002, the entire specification of which is incorporated herein by reference for all purposes as if fully set forth herein. This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2003-136158 filed May 14, 2003, the entire content of which is hereby incorporated by reference. 1. Field of the Invention The present invention relates to a steering control method for vehicles—especially electric vehicles—having four-wheel-independent steering. In particular, it relates to a vehicle steering control method for safely and smoothly operating a vehicle in a steering mode adapted to the constraints of passageways in facilities in which the vehicle is being driven, and to the placement of objects adjacent to those passageways. In the present application, the term ‘steering mode’ denotes a basic pattern of travel paths described by the wheels of a vehicle being steered. 2. Background Art Previously, in JP Patent Application No. 2001-351127, the inventors proposed a method for controlling operation of an electric vehicle with four-wheel-independent steering for steering in a wide variety of indoor/outdoor facilities such as hospitals, nursing homes, supply distribution bases, computer warehouses, large commercial facilities, libraries, sports/entertainment complexes, amusement parks, etc., by using steering modes adapted to conform to the constraints associated with the passageways in such indoor/outdoor facilities, and to the placement of objects in close proximity to the passageways. The specification of that prior JP Patent Application No. 2001-351127 describes how the steering of an electric vehicle in which steering/drive control is performed through separate drive motors and steering motors for each of its four wheels (left front, right front, left rear and right rear) in a number of different steering modes M The following equations were proposed as steering constraint condition equations (condition equations) for the above steering modes. For the M For the M For the M In the M and for a left turn: L:W:0 (E48)In the M
and for a left turn:
L (E58)where, in the above equations, - α
_{1 }is the steering angle for the right front wheel, - α
_{2 }is the steering angle for the left front wheel, - α
_{3 }the steering angle for the right rear wheel, - α
_{4 }is the steering angle for the left rear wheel, - n
_{1 }is the rotation speed for the right front wheel, - n
_{2 }is the rotation speed for the left front wheel, - n
_{3 }is the rotation speed for the right rear wheel, - n
_{3 }is the rotation speed for the left rear wheel, - L is the distance between each wheel and a center-line X between the front and rear wheels,
- W is the distance between each wheel and a center-line Y between the left and right wheels, and
- R, for the case in which the turning paths of the wheels inscribe concentric arcs, is the distance between the center of the concentric arcs and a point central to the locations of the four wheels (the distance from the center of the vehicle to the vehicle's center of rotation; i.e., the radius of vehicle rotation).
The problem with this, however, is that to change the vehicle's direction of travel, a steering command is issued with the distance R (vehicle turning radius) as a steering command value for increasing or decreasing the R setting of the existing steering command value, thus to cause the steering angles of the wheels (α For a driver actually operating this vehicle, it would be difficult to grasp, in an intuitive or physical sense, how the distance R is related to the steering angles of the wheels (direction of travel of the vehicle). Moreover, the value of the distance R can invert, going abruptly from −∞ to +∞ (full left to full right), or from +∞ to −∞ (full right to full left) with the direction of travel of the vehicle as the left/right dividing line. Therefore, from the standpoint of practical driving considerations, it would not be desirable to use such discontinuous changes in the distance R as a steering angle setting parameter for setting steering command values for the steering angles α The present invention was devised with the above problems in mind. It was devised to prevent the occurrence of [severe] toe-in/out phenomena in the steering process of a four-wheel-independent steering vehicle. Also, the present invention provides for the use of steering command values other than a distance R corresponding to the rotation radius (turning radius) of the vehicle. By using, instead of the distance R, an easily understandable steering command value such that the physical relationship between the steering command value and the vehicle's direction of travel will be reflected in the feel of the steering to a driver of the vehicle, the invention can prevent steering errors by drivers, and enable them to quickly and accurately steer the vehicle in the desired direction. It will also prevent collisions by preventing vehicles from taking off in the wrong direction when starting out from a stopped state, or when changing steering modes. In the present invention, to prevent [severe] toe-in/toe-out phenomena from occurring in a four-wheel-independent-steering vehicle steering process, steering control is performed wherein, by changing a steering command value, for changing the direction of travel of a vehicle by separately controlling steering angles α When synchronous or induction motors are used as wheel drive motors, steering is controlled by individually changing the steering angles α As one example of a steering command value that is actually used, for the case wherein the turning-vehicle-travel-paths of the wheels are concentric arcs, a distance R, which is the distance between a point central to the positions of the four wheels and a center point of said concentric arcs, is used as the command value. That is, steering control of a four-wheel-independent steering vehicle is effected such that by changing a steering command value, the direction of travel of a vehicle is changed by separately controlling the steering angles α Also, to control steering in a four-wheel-independent-steering vehicle in which the wheel drive motors are synchronous or induction motors, for case wherein the turning-vehicle-travel-paths of the wheels are concentric arcs, a steering command value is defined as a distance R, which is the distance between a point central to the positions of the four wheels, and a center point of said concentric arcs, in a process for changing the command value R from a value R Also, steering constraint condition equations for forming prescribed steering modes are disclosed. As examples, equations for two steering modes that would probably be used as the prescribed mode most often will be presented. One of these is a mode in which, during turns, the left and right rear wheels follow in the travel paths of the left and right front wheels, respectively (referred to herein as ‘steering mode M For forming the steering mode M
and
and for forming the steering mode M where α
L is the distance between the wheels and a center line X between the front wheels and rear wheels; W is the distance between the wheels and a center line Y between the left wheels and right wheels; and R, which is used as the command value, is the distance between a point central to the positions of the four wheels and a center point of said concentric arcs. Note that when there is no need to forcibly control the speeds of rotation n Also, in the present invention, a command value that conforms more closely to the driver's sense of steering direction is used, thus preventing driver operation errors, and enabling the driver to steer in the desired direction with greater certainty. That is, instead of using the distance R (a distance equivalent to the turning radius of the vehicle) as the command value, either an angle an, which is the angle formed between a center line Y (the center line between the left wheels and right wheels of the vehicle) and the direction of travel of a point Pn (an arbitrarily located point on the vehicle); or an angle α That is, in the present invention, steering control of a four-wheel-independent-steering vehicle is performed such that in steering control wherein, by changing how a steering command value taken for changing the direction of travel of a vehicle by separately controlling steering angles α Also, as an alternative, steering control of a four-wheel-independent-steering vehicle may be performed such that in steering control wherein by changing how a steering command value is taken for changing the direction of travel of a vehicle by separately controlling steering angles α Then, with the steering command value defined as the angle αn, the steering constraint condition equations for forming a prescribed steering mode M
and the steering constraint condition equations for forming a prescribed steering mode M
where
n L is the distance between the wheels and a center line X between the front wheels and rear-wheels; W is the distance between the wheels and a center line Y between the left wheels and right wheels; x α Note that when there is no need to forcibly control the speeds of rotation n Also, in the present invention, steering control of a four-wheel-independent-steering vehicle may be performed such that in steering control wherein, by changing how a steering command value is taken, for changing the direction of travel of a vehicle by separately controlling steering angles α Also, as an alternative, steering control of a four-wheel-independent-steering vehicle may be performed such that in steering control wherein, by changing how a steering command value is taken, for changing the direction of travel of a vehicle by separately controlling steering angles α Then, with the steering command value defined as the angle α
and the steering constraint condition equations for defining a prescribed steering mode M
where
L is the distance between the wheels and a center line X between the front wheels and rear wheels; W is the distance between the wheels and a center line Y between the left wheels and right wheels; and α Note that when there is no need to forcibly control the speeds of rotation n In addition, in the present invention, in order to prevent collisions from occurring when the vehicle is started into motion from a stopped state, or when the steering mode is changed, and to ensure that the vehicle moves off smoothly and accurately in the desired direction, operating in the prescribed steering mode, when a change is made from one to another of a plurality of steering modes including the forward and reverse modes of the vehicle, the steering angles of the wheels, α Also, when a change is made to select a desired steering mode from a plurality of prescribed modes including the forward and reverse modes of the vehicle, the vehicle is driven in motion only after the steering angles of the wheels, α These and other features, aspects, and advantages of the present invention will become apparent with reference to the following description, claims, and accompanying drawings, where The best mode for carrying out the present invention is described in detail below, with reference to the attached drawings. One basic mode for carrying out the present invention is a four-wheel-independent-steering-vehicle steering control method that constitutes steering control wherein, by changing a steering command value, for changing the direction of travel of a vehicle by separately controlling steering angles α incremental transition steering angles [α the steering angles α after the steering angles α the steering angles α from this point on, after steering angle conformance of the steering angles α Another basic mode for carrying out the present invention is a four-wheel-independent-steering-vehicle steering control method that constitutes steering control wherein, by changing how a steering command value is taken for changing the direction of travel of a vehicle by separately controlling steering angles α incremental transition steering angles [α the steering angles α after the steering angles α the steering angles α from this point on, after steering angle conformance of the steering angles α In the following paragraphs, the present invention will be described with reference to drawings showing an embodiment thereof. The speeds of rotation of the right front wheel When the vehicle is under steering control, each individual rotation speed n The steering mode M
In steering mode M Steering mode M where
and where it is assumed that d=0 because the vehicle is operated at low speed. Steering mode M When the vehicle is turned clockwise, with the right rear wheel point P W (E44)Where
When the vehicle is turned counter-clockwise, with the left rear wheel point P where
Steering mode M When the vehicle is turned clockwise, with the right front wheel point P where
When the vehicle is turned counter-clockwise, with the left front wheel point P L (E58)where
Because the separate paths traveled by the four wheels in the modes M Accordingly, provided in the vehicle is a wheel steering angle computation means containing in its memory a computation program for computing wheel steering angles α a computation program for computing wheel steering angles α a computation program for computing wheel steering angles α a computation program for computing wheel steering angles α a computation program for computing wheel steering angles α Also provided in the vehicle is a wheel rotation speed computation means containing in its memory a computation program for computing wheel rotation speeds n a computation program for computing wheel rotation speeds n a computation program for computing wheel rotation speeds n a computation program for computing wheel rotation speeds n a computation program for computing wheel rotation speeds n In the present invention, the steering process of a four-wheel-independent steering vehicle is controlled while the vehicle is moving, such that steering constraint condition equations as described above will always be satisfied, and the occurrence of wheel toe-in/out phenomena will be prevented. To accomplish this ‘steering command values’ for setting and changing the steering angles (α For example, in steering mode M
Here, there are five variables, at, α For another example, in steering mode M Here there are three variables, α If the distance R and steering angles α One way to maintain steering angle conformance would be for the driver, when changing the distance R (the steering command value) to a new steering command value (distance), thus to change the steering angles α In other words, the steering control method of the present invention is characterized in that, in steering control wherein, by changing a steering command value, the direction of travel of a vehicle is changed by separately controlling the steering angles α incremental transition steering angles [α the steering angles α when the steering angles α the steering angles α from this point on, proceeding in the same manner as above, when steering angle conformance of the wheel steering angles α the steering angles α when the steering angles α Next, we will consider the sensitivity of wheel steering angles α with respect to the steering command value distance R (vehicle turning radius) in steering mode M If y=tan
and if
then
Similarly,
If we solve equation (1) and equation (2) for the values W=0.5 m and L=1 m, the results are as shown in Thus the sensitivity of the wheel steering angles α to the distance R (the vehicle rotation radius/steering command value) varies widely depending on the value of R. The distance R per se is therefore not a good value to use as the steering command value. A possible consideration would be to introduce distance R as a function of time, R=f (t), and to control wheel steering angles α through the function R=f(t). The function is introduced as follows: Equation (1) is transformed as follows:
Similarly,
Then, setting
(Where K=constant value)
Accordingly, we then have
Then by applying formula (3) we eventually arrive at Equation (13); i.e., Here, if we set R=0 W=0.5 L=1 and t=0, the integration constant CL is CL=0.463648 (rad). Accordingly, if K=π/20, then
Thus the distance R can be varied as a function of time t in Equation (13). When this is done, the right front wheel steering angle α
As described above, although using the distance R as the steering command value simplifies theoretical development, when it comes to a driver actually controlling the steering, it would definitely make steering operations difficult. The difference in sensitivity dα/dR at low and high values of distance R is in the double digits. Also, in the range of steering angles near the straight forward direction of the vehicle where, in actual driving, the frequency [of steering events] is highest, the sensitivity dα/dR is high, making the steering hyper-sensitive. Also, the distance R value could abruptly invert between −∞ and +∞ or between +∞ and −∞. Moreover; since the distance R is the distance to the center-of-rotation in the lateral direction of the vehicle, for the driver, it would be very difficult to associate this with an actual ‘feel’ for the steering of the vehicle. These factors make operation extremely difficult for the driver. Therefore, in the present invention, instead of the distance R, the angle α That is, in steering mode M
Then by substituting equation (18) in equations (E11), (E12), and (E13), the relationship between the steering angles α
In steering mode M
By substituting equation (23) in equations (E31), (E32), and (E34), the relationship between the steering angles α
The relationships between the angle α Also, instead of this center point Po (described above), an angle α When the angle α
For steering mode M
For steering mode M
As is clear from the above examples, according to the four-wheel-independent-steering vehicle steering control method of the present invention, wherein one of the variables of a steering constraint condition equation for forming a prescribed steering mode is defined as the steering command value S; in a process for changing the steering command value S from a value S incremental transition steering angles [a the steering angles α the wheel steering angles α thus preventing the occurrence of severe wheel toe-in/out phenomena in the vehicle steering process. Also, according to the present invention, a steering angle α Also, according to the present invention, when the vehicle is started out from a stop, or when the prescribed steering mode is changed, the steering angles α Also, according to the present invention, when the vehicle is just starting out or is changing modes, it does so only after the steering angles of the wheels α The foregoing describes preferred embodiments of the invention. A variety of modifications could be made, however, without deviating from the scope of the invention as defined by the following claims: Patent Citations
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